1. Field of the invention:
The invention relates to an installation and a method for refrigeration using a reversible sorption system, especially for freezing various products or for producing chilled water or ice.
2. Description of the Related Art
Heat generation or refrigeration installations based on a liquid/gas phase change or on reversible sorption between a gas, called the working gas, and a liquid or solid sorbent, are known. A reversible sorption may be an absorption of a gas by a liquid, an absorption of a gas on a solid, or a reaction between a gas and a solid. A reversible sorption between a sorbent S and a gas G is exothermic in the synthesis direction S+G→SG and is endothermic in the decomposition direction SG→S+G. In a liquid/gas phase change of the gas G, the condensation is exothermic and the evaporation is endothermic.
These reversible phenomena can be represented on a Clausius-Clapeyron plot by their equilibrium line:
            ln      ⁢                          ⁢      P        =          f      ⁡              (                              -            1                    /          T                )              ,            more      ⁢                          ⁢      precisely      ⁢                          ⁢      ln      ⁢                          ⁢      P        =                  -                              Δ            ⁢                                                  ⁢            H                    RT                    +                        Δ          ⁢                                          ⁢          S                R              ,P and T being the pressure and the temperature, respectively, ΔH and ΔS being the enthalpy and the entropy of the phenomenon (decomposition, synthesis, evaporation, condensation) involved, respectively, and R being the perfect gas constant.
The endothermic step may be advantageously employed in an installation of this type for freezing various products (especially water for obtaining ice) or for producing chilled water.
Thus, EP 0 810 410 discloses a system comprising a reactor and an evaporator/condenser connected via a pipe provided with a valve. A thermochemical reaction or a solid/gas adsorption takes place in the reactor. The latter includes means for heating the solid that it contains and means for extracting the heat from the exothermic synthesis reaction, these means being formed either by a heat exchanger, or by increasing the thermal mass of the reactor. The reactor is designed in such a way that, with its content, it has a thermal mass sufficient to absorb the heat produced during the exothermic reaction. The method of managing this system consists in bringing the evaporator/condenser into communication with the reactor when the evaporator/condenser is filled with the working gas in liquid form, this having the effect of cooling the evaporation/condenser by evaporation, and then in turning on the means intended to heat the solid so as to deliver the gas to the evaporator/condenser and to condense it therein. The means intended to heat the solid in the reactor are turned on before the previous step has been completed. The refrigeration produced by the evaporator/condenser can be used to produce chilled water or ice. However, in this system, the cycle times are relatively long because the regeneration of the system takes place at a high temperature TH and the cooling of the reactor takes place at ambient temperature To. Consequently, the reactor undergoes a relatively large thermal excursion between the regeneration temperature and the ambient temperature. This results in a low performance coefficient.
The object of the present invention is to provide a device having a very high refrigeration power per unit volume, for example around 200 kW/m3, at a relatively low working temperature TU and with greatly reduced cycle times and greater performance. The term “working temperature” is understood to mean temperature of freezing products (the freezing of water, to produce ice, or the freezing of other products) or the temperature to which it is desired to lower the products, and to maintain them at this temperature, without freezing them (for example in order to obtain chilled water).